Selective signaling system



G. K. THOMPSON. SELECTIVESIGNALING SYSTEM. APPLICATION HLED JAN. 15, I920.

1 ,398,287 Patented Nov. 29, 1.921;

1N VEN TOR.-

ATTOR'NEY UNETEE STATES earner QFPEtCBE.

GEORGE K. THOMPSON, OF EIAPLEWOOD, NEW JERSEY, ASSIGNOR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SELECTIVE SIGNALING SYSTEM.

Specification of Letters Patent.

Application filed January 15, 1920. Serial No. 351,604.

To all whom it may concern:

Be it known that I, Gnoncn K. THOMPSON, residing at Maplewood, in the county of sex and State of New Jersey, have invented certain Improvements in Selective Signaling Systems, of which the following is a specification.

This invention relates to selective signaling systems, particularly to systems of the character which are adapted for use in connection with multi-station telephone lines.

It is an object of this invention to provide means for selectively signaling over a common battery line, by the use of currents differing in frequency and polarity, without necessitating the grounding of the line conductors at the subscribers stations.

This object of the invention and certain other features thereof set forth below, are attained as described in the following specification which has reference to a certain specific form of embodiment of the invention illustrated in the accompanying draw-' ing, in which Figure 1 is a diagrammatic view of one form and arrangement of circuits embodying the invention and Fig. 2, a graph showing the wave form of the current which may be caused to flow through the circuits of Fig. 1.

Reference character L in the drawing designates a telephone line having associated therewith four subscriberssubstations S S S and S, which may be of any of the types commonly employed and which are shown conventionally in the drawing for sake of simplicity. Associated with the substations and bridged across the line conductors are signalin devices illustrated as bells designated B B B and 13,, the former two of which are responsive only to current of one frequency, herein assumed as 20 cycles, and the latter two of which, to current of another frequency, 40 cycles, it being un derstood that any other suitable frequencies may be used. Bells B and B are biased negatively 2'. 6., so constructed that they respond only to current of negative polarity and bells B and B, are biased positively. In series with the bells are condensers 5 which serve to prevent the flow of battery current through the bells which current would otherwise cause decreased marginal operation of line and supervisory signal circuits (not shown).

The line terminates at the central otiice in a jack J which is adapted to receive the plug P of an operators cord, only one terminal of which has been illustrated in the drawing, it being understood that the cord is equipped with the common battery and the supervisory signaling apparatus usual in the art. The cord is also provided with a set of keys K K K and K, arranged for signalin selectively to the subscribers substations S S S and S,, respectively. The keys are for this purpose associated with generators G and G which may be of the type illustrated in the patent to Stanley S. A. Watkins for signaling system, No. 1,249,- 570 dated December 11, 1917. The waves of electromotive force of these generators are such that when the same are applied to a bell having a condenser in series therewith the current therethrough has a wave shape of substantially the form illustrated in Fig, 2. It will be observed in this diagram that the maximum ordinate in one direction or loop is far greater than that of the opposite direction, although the total current in one direction is equal to the current in the other direction, so that the average value of the current per cycle is zero. Each generator is provided with three terminals, and the .windings'are so arranged that the electromotive force between terminals 1 and 2 has a high negative ordinate whereas that between i 1 and 3 has a high positive ordinate. The frequency of generator G, corresponds to that of bells B and B and the frequency of G corresponds to that of B and B,, as indicated in the drawing.

To ring the subscribers station S the operator associates the plug of her cord with the jack J and depresses the key K so that current of a frequency of 20 cycles and a larger negative than positive ordinate flows into line L and through the bells. B and B fail to respond because of the frequency of the current and bell B fails to operate because the maximum value of positive current is insufficient to overcome its bias. The bell B however, being of the right periodicity and bias responds to the current. The other substations on the line may be signaled selectively in similar manner by the remaining keys.

it will be observed that because of the connection of the bells across the line conductors inductive disturbances are avoided which would be presentunder certain line Patented Nov. 29, 1921.

ordinates, which difference is not sufiicient to operate selectively biased bells having commercial adjustments. The current used herein has, however, the maximum ordinate far larger in one direction than in the other which permits of the selectiveoperation of biased bells having commercial adjustments. The operation of this system depends therefore on the peculiar shape of the current wave and the selective feature is secured by the frequency as well as the direction of the maximum value of the current.

Although I have herein shown and de scribed only one form and arrangement of apparatus I embodying the invention it is readily understood that various changes and modifications may be made therein within the scope of the following claims, without departing from the spirit and scope of the invention.

What is claimed is:

l. In a selective signaling system, line conductors, biased frequency selective signaling devices associated therewith, condensers in series with said devices, and means for associating with said line current of one fre-.

quency or another, having a larger ordinate in one directionthan in'the other.

2. In a selective signaling system, line conductors, a plurality of biased signaling devices bridged across said conductors, certain of said devices being responsive to currents of one frequency and others to current of another frequency, condensers in series with said devices, a plurality of sources of current for said system, certain of said sources being of said one frequency and others of said other frequency, the current from each of the sources having an average value substantially equal to zero but a larger ordinate in one direction than in the other, and means for selectively associating said sources with the line.

3. In a common battery telephone system, line conductors, a pair of oppositely biased signaling devices bridged across said conductors and responsive to one frequency, a

'second pair of oppositely biased signaling devices bridged across said conductors but responsive to another frequency, a generator of said one frequency for causing in said line currents having an average value of zero per cycle but a larger ordinate in one direction than in the other, means for associating said generator with the line with the larger ordinateselectively' in one direction or the other, a second generator similar to the first mentioned one'but havingsaid other frequency, and means for associating said second generator with the line with the larger ordinate of current selectively in one direction or the other.

I. In a selective signaling system, line conductors, biased signaling devices associated therewith, said signaling devices be- "ing directly selective to frequencies in pairs,

respective condensers in series with said devices, and means for associating with said line current of one frequency or another having a larger ordinate in one direction than in the other.

In testimony whereof I have-signed my name to this specification. this lath day of January, 1920.

GEORGE K. THOMPSON. 

